The present invention relates to a hologram-image recording apparatus and method for producing holographic stereogram which is capable of producing a three-dimensional rendition of either a photograph or an image produced by a computer.
A holographic stereogram is produced by imaging two pictures of a single object obtained by sequentially photographing the object from different observing points. These two pictures are sequentially exposed and recorded on one hologram recording medium as a collection of oblong or dot shaped elements. A user can identify a two-dimensional image, including an aggregate of image information of a portion of the hologram, when the user looks at the holographic stereogram through one eye from a certain position. When the user looks at the holographic stereogram from another position, the user can see a two-dimensional image, including an aggregate of image information of another portion of the hologram. Therefore, when the user looks at the holographic stereogram with both eyes, the parallax between the two eyes causes the recorded hologram to be observed as a three-dimensional image.
Such a holographic stereogram can be produced by a holographic stereogram producing apparatus 100 shown in FIG. 12 (A). Holographic stereogram producing apparatus 100 includes a laser-beam source 101 for emitting a single wavelength laser beam L10 exhibiting excellent coherency, and a partial reflecting mirror 102 for splitting laser beam L10 into an object laser beam L11 and a reference laser beam L12. Optical elements 103 to 107 comprise an optical system for acting upon object laser beam L11, and a transmissive LCD display unit 108 is also provided for further acting upon object laser beam L11. Optical elements 109 to 111 comprise an optical system for acting upon reference laser beam L12. Finally, an electromotive stage 113 is provided for holding a hologram recording medium 112 upon which object laser beam L11 and reference laser beam L12 converge, and for moving hologram recording medium 112 as required.
The optical system for acting upon object laser beam L11 includes the following optical elements sequentially disposed along the optical axis of the path of object laser beam L11. A total reflection mirror 103 is first provided for changing the direction of beam L11. Beam L11 then passes through a first cylindrical lens 104 that diffuses beam L11 in a one dimensional direction. A collimator lens 105 receives beam L11 and forms beam L11 into a plurality of parallel laser beams. A projecting lens 106 and a second cylindrical lens 107 are also provided for guiding beam L11 to hologram recording medium 112. Display unit 108 is disposed along the light path of beam L11, and comprises a transmission type liquid crystal panel disposed between the collimator lens 105 and the projecting lens 106. Image data output from an image processing portion (not shown) is displayed on the display unit 108.
The optical system for acting upon reference laser beam L12 includes the following optical elements sequentially disposed along the optical axis of the path of reference laser beam L12. A cylindrical lens 109 is first provided for diffusing beam L12 in a one dimensional direction. Beam L12 then passes to a collimator lens 110 that forms diffused beam L12 into a plurality of parallel laser beams. A total reflection mirror 111 for changing the transmission direction of reference laser beam L12 to arrive at hologram recording medium 112 is also provided.
Hologram recording medium 112 comprises, for example, a photosensitive film. As shown in FIG. 12 (B) as well as FIG. 12(A), medium 112 is held by an electromotive stage 113. When electromotive stage 113 is moved, medium 112 is intermittently moved as desired in a direction indicated by an arrow b.
During operation, laser beam L10 is emitted from laser-beam source 101 and is incident on half mirror 102, as shown in FIG. 12(A). Half mirror 102 splits laser beam L10 into object laser beam L11 and reference laser beam L12. Object laser beam L11 is incident on display unit 108 through first cylindrical lens 104 and collimator lens 105. When object laser beam L11 passes through display unit 108, object laser beam L11 is image-modulated in accordance with to an image displayed on display unit 108. Modulated object laser beam L11 is incident on recording medium 112 after passing through projecting lens 106 and second cylindrical lens 107. Reference laser beam L12 is incident on recording medium 112 through the optical system composed of cylindrical lens 109, collimator lens 110 and total reflection mirror 111. Interference fringes generated between the reference beam and the modulated object beam are sequentially recorded in the form of oblong or dot shapes on recording medium 112. These recorded interference fringes form the hologram.
Vibrations exerted on the hologram recording medium 112 disposed in the exposing and recording portion P100 when each hologram is exposed and recorded may have an adverse influence on the produced holographic stereogram. That is, the holographic stereogram producing apparatus 100 may encounter this problem when small vibrations on the order of the wavelength of the laser beam L10 are exerted on the recording medium 112. As a result of such problem, the state of interference fringes which are sequentially exposed and recorded on the recording medium 112 may become instable and a portion of the hologram which are exposed and recorded may encounter a phenomenon wherein the diffraction efficiency and brightness deteriorate. If greater vibrations are exerted on the holographic stereogram producing apparatus 100, the exposing and recording of the hologram on the recording medium 112 may not be able to be performed.
When a portion of the hologram have been exposed and recorded on the recording medium 112 wherein the diffraction efficiency is unsatisfactorily low due to the influence of vibrations or the like, such portion of the hologram may be in a dark state upon performing a reproducing operation. Accordingly, in such situation, uniformity of the images deteriorates.
As a result, the holographic stereogram producing apparatus 100 is generally provided with a vibration isolator for isolating external vibrations and quickly attenuating exerted vibrations so as to enable an element hologram to be stably exposed and recorded on the recording medium 112. The vibration isolator may include an air damper or springs appropriately disposed between a substrate on which the laser-beam source 101 and the optical elements of the optical system have been mounted and the case of the apparatus. Such vibration isolator may effectively prevent external vibrations.
Additionally, the holographic stereogram producing apparatus 100 should prevent vibrations of the recording medium 112 which may be exerted by a guide means and a moving means for holding and moving the recording medium 112. The guide means and the moving means should secure the recording medium 112 so as to prevent small vibrations which may correspond to the wavelength of the laser beam L10 during exposing and recording of the hologram on the recording medium 112 which is performed in the exposing and recording portion P100. When the exposing and recording of the hologram on the recording medium 112 has been completed, the guide means and the moving means may quickly move the recording medium 112. When the recording medium 112 which has been moved for a predetermined distance is stopped, vibrations may be created which should be quickly damped or attenuated.
However, in the holographic stereogram producing apparatus 100, it may take approximately two seconds for vibrations created due to the movement and stopping of the recording medium 112 to be attenuated after the recording medium 112 has been stopped. Therefore, the holographic stereogram producing apparatus 100 may need a relatively long time period to dampen the vibrations of the recording medium 112 whenever the electromotive stage 113 is used to expose and record a hologram. As a result, a relatively large amount of time may be needed to produce one holographic stereogram.
Therefore, the holographic stereogram producing apparatus may be provided with a moving mechanism incorporating a guide and a moving apparatus in place of the foregoing electromotive stage 113 for preventing vibrations of the hologram recording medium 112. The recording medium 112 is disposed on two parallel rollers each having a predetermined tension imparted thereon by a torsion coil spring or the like. The object laser beam L11 and the reference laser beam L12 are incident on the recording medium 112 while an optical element is being pressed against the recording medium 112. Only 1/4 of the time or less may be required for damping vibrations created by the movement of the recording medium 112. However, such a guide and a moving apparatus require complicated structures.
The holographic stereogram producing apparatus 100 may incorporate another moving mechanism which does not employ a torsion coil spring. In this case, a motor constantly inversely rotates a slip member. The force of these rotations are transmitted to one of the parallel rollers so as to generate a predetermined torque. However, such motor may be rotated during an exposing and recording operation, whereupon internal vibrations may be created. Thus, the hologram being exposed and recorded may become instable. As a result, the quality of the produced holographic stereogram deteriorates.